The bearings will be fine if they are even half decently sealed, but I soon learnt on my first trip that the dust and rain (really!) soon stripped the lubrication from the chain. I waded the Nyidalur ford on the Sprengisandur on foot in big water prior to driving it in the hired 4×4, it was no worse than other river crossings I have done here in the UK tbh. The worst fords were the Svarta just of the Kjolur (my first deepish one, approx 60cm of slow water) and the Hnottottaalda on the F26 (Sprengisandur) closeish to Versalir. Versalir was closed the last time I visited there two years ago but was a really welcome place previously. The Hnottottaalda ford has a rock step in it that caught me out and almost caused some damage.
There are no fords to consider on the actual Kjolur route but if staying at the Hvitarnes hut the Svarta will need to be crossed.
The Kortabok road atlas is excellent for touring, it shows all the fords. None are shown between Myvatn and where it joins the Sprengisandur at Bjarnastadir. Happy days 🙂